This could certainly be pregnancy, as someone stated above. If you are sexually active, take a pregnancy test or see your doctor about having one done.
Another possibility is something called benign paroxysmal positional vertigo. It is a benign (safe) condition caused by tiny crystals in the inner ear getting stuck in the wrong place. This causes intermittent severe dizziness when you change your position or even roll over in bed. If this sounds like what is happening, you should see your doctor for diagnosis and treatment (a series of maneuvers that involves moving your body and head in certain ways to dislodge the crystals from wherever they are stuck).
You could aso have your thyroid checked, by having an underactive thyroid also has other signs, such as weight gain, constipation, hair and skin changes, etc. It also usually doesn't come on acutely.
Maybe you are working too hard and stressing yourself out, I would take a day off for a breather, Just sounds like stress.
There is a veriety of problems that can cause this. Stress, pregnancy, insomnia, sleep disorders. You should probably take a home pregnancy test and if it is negative then you should see a doctor.